I got out early today hoping to get a few favorable rays of sun - overcast and windy. I waited and waited. The wind died down for about 5 minutes. During that time the sun came out for less than a minute, but enough time to capture a few improved images of this mystery fruit. I tried to trace the vine to find some leaves, but they had all dried up and were indistinguishable from the other dead vegetation on the ground. What is it??? I did pick one not in this image - there were 4 fruits altogether. Later today I'll slice it in half and try to photograph it. In this photo the fruit appear to be more red; however, when I picked one of the fruit and brought it inside, it appeared more orange in color.
It's not a mystery anymore. It's passion flower fruit. It's also native to a narrow band along the south Texas border. That makes this one about 350-400 miles north of its native habitat. As it was found along a fence row a probable explanation is that a migratory bird ate one or more seeds in the plant's natural habitat, flew north, sat on the fence and excreted the seed where it grew to produce these fruit out of it's natural area - a rather good example of seed dispersal by a bird.